Most standards used to regulate communications from wireless devices to base stations require that each wireless device control how much power is emitted from the wireless device when transmitting a radio frequency signal to the base station. As used herein a wireless device refers generally to portable and mobile wireless devices that use radio frequency signals to transmit and receive information. For instance, wireless devices refers to, but is not necessarily limited to, cellular telephones, personal communication systems phones, radiotelephone handsets, personal digital assistants, and other current and future wireless handsets.
These communication standards are instituted to ensure that when different wireless devices transmit signals to a particular base station, the base station receives the signals at relatively the same power level. Otherwise, if some wireless devices emit signals with higher power levels than other wireless devices to the same base station, the signals with the higher power levels can swamp (i.e., inundate, overtake, or overpower) signals with lower power levels.
Accordingly, power levels for signals emitted by a wireless device are dynamically controlled over various power level ranges dependent upon various factors, such as how far away the wireless device is from the base station. For example, the closer a wireless device is to a base station, the less power the transmit signals need in order to maintain a consistent received-signal power level when the signals are received at the base station. On the other hand, the farther away a wireless device is from a base station, the more power the transmit signals need in order to maintain a consistent received-signal power level at the base station.
The key components used to control the power level of signals emitted by wireless devices are a radio frequency (RF) power amplifier and a control circuit used to set the power level of the power amplifier. The power amplifier is primarily used to amplify power levels of signals generated by a transmit module of the wireless device before the signals are transmitted by an antenna. The control circuitry typically adjusts the power levels produced by the RF power amplifier through a feedback loop.
The feedback loop typically includes an RF directional coupler and a detector diode connected to an output terminal of the power amplifier for the purpose of transferring a voltage measurement indicative of the power level produced by the power amplifier back to the control circuitry. The power level feedback enables the control circuitry to directly monitor and adjust the power level produced by the power amplifier, i.e., boost, maintain, or reduce the power level produced by the power amplifier.
In some implementations, it is possible to measure the current produced at the output of the power amplifier as means for monitoring the power level produced by the power amplifier. This may be accomplished through the use of a current sensing resistor coupled to the output of the power amplifier.
In either of the implementations, power losses are attributable to the directional coupler/detector diode or the sensing resistor. These power losses reduce the battery life of a wireless device, which in turn reduces the usage time (standby and communication time (e.g., talk time)) for a user of the wireless device. Additionally, these circuitry components (i.e., directional coupler/detector diode or sensing resistor) add to the overall cost to manufacture a wireless device. Furthermore, most wireless device manufactures strive to reduce the size and weight of the wireless devices; however, these circuitry components increase the overall size of a wireless device, because they increase the parts count associated with the wireless device.